It is known to use a storage tank to store a processed fluid produced by a fluid treatment system. For example, reverse osmosis systems are used to produce potable or drinking water from water sources that contain undesirable contaminants, etc. In a typical reverse osmosis system, especially in the type of reverse osmosis system used in homes, the rate at which treated water or “permeate” is produced by the system can be very low. As a result, a storage tank is used to store permeate, so that relatively large quantities can be made available when the consumer opens the tap or faucet. In the past, “precharged” storage tanks are used. In this type of storage tank, a bladder is used to define a pressurized chamber, usually filled with a compressible gas, such as nitrogen. The bladder isolates the gas from the processed water received by the tank. As processed water or “permeate” (in the case of a reverse osmosis system) is it received by the tank, it gradually compresses the gas in the pressurized chamber. As a result, the permeate is stored under pressure, such that when the tank is opened, the pressure in the storage tank exerted by the compressed gas, forces permeate out of the tank and to the faucet.
Although these storage tanks are widely used and provide a suitable means for storing permeate, they do have a significant drawback. As more and more permeate is received by the tank, the pressure needed to effect flow of permeate into the tank increases because as the gas chamber is compressed, forces on the bladder increase. Accordingly, in order to completely fill the storage tank, a significant pressure must be applied to the permeate as the capacity of the tank is reached. This resistance to flow exerted by the tank in itself decreases production rate of the reverse osmosis system, since the reverse osmosis system relies on differential pressures between the source and the output to effect flow across the membrane. In addition, as permeate is discharged by the tank, its delivery pressure is gradually reduced as the pressurized gas chamber expands. As a result, the delivery pressure varies significantly between a full tank and a nearly empty tank.
The assignee of the present invention manufactures and sells a reverse osmosis filtration system the includes a flushing feature that periodically flushes the input of the R/O membrane with permeate to cleanse the membrane. The flushing feature is implemented using a flushing system control circuit that selectively places a flushing accumulator that stores permeate in communication with the input of the R/O membrane. The flushing system control circuit and accumulator are housed within a replaceable cartridge that also contains the R/O membrane.